Lucene example source code file (OpenBitSetIterator.java)

This example Lucene source code file (OpenBitSetIterator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

docidsetiterator, docidsetiterator, no_more_docs, no_more_docs, openbitsetiterator, openbitsetiterator, override, override

The Lucene OpenBitSetIterator.java source code

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.lucene.util;

import org.apache.lucene.search.DocIdSetIterator;

/** An iterator to iterate over set bits in an OpenBitSet.
 * This is faster than nextSetBit() for iterating over the complete set of bits,
 * especially when the density of the bits set is high.
 */
public class OpenBitSetIterator extends DocIdSetIterator {

  // The General Idea: instead of having an array per byte that has
  // the offsets of the next set bit, that array could be
  // packed inside a 32 bit integer (8 4 bit numbers).  That
  // should be faster than accessing an array for each index, and
  // the total array size is kept smaller (256*sizeof(int))=1K
  protected final static int[] bitlist={
    0x0, 0x1, 0x2, 0x21, 0x3, 0x31, 0x32, 0x321, 0x4, 0x41, 0x42, 0x421, 0x43, 
    0x431, 0x432, 0x4321, 0x5, 0x51, 0x52, 0x521, 0x53, 0x531, 0x532, 0x5321, 
    0x54, 0x541, 0x542, 0x5421, 0x543, 0x5431, 0x5432, 0x54321, 0x6, 0x61, 0x62, 
    0x621, 0x63, 0x631, 0x632, 0x6321, 0x64, 0x641, 0x642, 0x6421, 0x643, 
    0x6431, 0x6432, 0x64321, 0x65, 0x651, 0x652, 0x6521, 0x653, 0x6531, 0x6532, 
    0x65321, 0x654, 0x6541, 0x6542, 0x65421, 0x6543, 0x65431, 0x65432, 0x654321, 
    0x7, 0x71, 0x72, 0x721, 0x73, 0x731, 0x732, 0x7321, 0x74, 0x741, 0x742,
    0x7421, 0x743, 0x7431, 0x7432, 0x74321, 0x75, 0x751, 0x752, 0x7521, 0x753, 
    0x7531, 0x7532, 0x75321, 0x754, 0x7541, 0x7542, 0x75421, 0x7543, 0x75431, 
    0x75432, 0x754321, 0x76, 0x761, 0x762, 0x7621, 0x763, 0x7631, 0x7632, 
    0x76321, 0x764, 0x7641, 0x7642, 0x76421, 0x7643, 0x76431, 0x76432, 0x764321, 
    0x765, 0x7651, 0x7652, 0x76521, 0x7653, 0x76531, 0x76532, 0x765321, 0x7654, 
    0x76541, 0x76542, 0x765421, 0x76543, 0x765431, 0x765432, 0x7654321, 0x8, 
    0x81, 0x82, 0x821, 0x83, 0x831, 0x832, 0x8321, 0x84, 0x841, 0x842, 0x8421, 
    0x843, 0x8431, 0x8432, 0x84321, 0x85, 0x851, 0x852, 0x8521, 0x853, 0x8531, 
    0x8532, 0x85321, 0x854, 0x8541, 0x8542, 0x85421, 0x8543, 0x85431, 0x85432, 
    0x854321, 0x86, 0x861, 0x862, 0x8621, 0x863, 0x8631, 0x8632, 0x86321, 0x864, 
    0x8641, 0x8642, 0x86421, 0x8643, 0x86431, 0x86432, 0x864321, 0x865, 0x8651, 
    0x8652, 0x86521, 0x8653, 0x86531, 0x86532, 0x865321, 0x8654, 0x86541, 
    0x86542, 0x865421, 0x86543, 0x865431, 0x865432, 0x8654321, 0x87, 0x871, 
    0x872, 0x8721, 0x873, 0x8731, 0x8732, 0x87321, 0x874, 0x8741, 0x8742, 
    0x87421, 0x8743, 0x87431, 0x87432, 0x874321, 0x875, 0x8751, 0x8752, 0x87521, 
    0x8753, 0x87531, 0x87532, 0x875321, 0x8754, 0x87541, 0x87542, 0x875421, 
    0x87543, 0x875431, 0x875432, 0x8754321, 0x876, 0x8761, 0x8762, 0x87621, 
    0x8763, 0x87631, 0x87632, 0x876321, 0x8764, 0x87641, 0x87642, 0x876421, 
    0x87643, 0x876431, 0x876432, 0x8764321, 0x8765, 0x87651, 0x87652, 0x876521, 
    0x87653, 0x876531, 0x876532, 0x8765321, 0x87654, 0x876541, 0x876542, 
    0x8765421, 0x876543, 0x8765431, 0x8765432, 0x87654321
  };
  /***** the python code that generated bitlist
  def bits2int(val):
  arr=0
  for shift in range(8,0,-1):
    if val & 0x80:
      arr = (arr << 4) | shift
    val = val << 1
  return arr

  def int_table():
    tbl = [ hex(bits2int(val)).strip('L') for val in range(256) ]
    return ','.join(tbl)
  ******/

  // hmmm, what about an iterator that finds zeros though,
  // or a reverse iterator... should they be separate classes
  // for efficiency, or have a common root interface?  (or
  // maybe both?  could ask for a SetBitsIterator, etc...

  private final long[] arr;
  private final int words;
  private int i=-1;
  private long word;
  private int wordShift;
  private int indexArray;
  private int curDocId = -1;

  public OpenBitSetIterator(OpenBitSet obs) {
    this(obs.getBits(), obs.getNumWords());
  }

  public OpenBitSetIterator(long[] bits, int numWords) {
    arr = bits;
    words = numWords;
  }

  // 64 bit shifts
  private void shift() {
    if ((int)word ==0) {wordShift +=32; word = word >>>32; }
    if ((word & 0x0000FFFF) == 0) { wordShift +=16; word >>>=16; }
    if ((word & 0x000000FF) == 0) { wordShift +=8; word >>>=8; }
    indexArray = bitlist[(int)word & 0xff];
  }

  /***** alternate shift implementations
  // 32 bit shifts, but a long shift needed at the end
  private void shift2() {
    int y = (int)word;
    if (y==0) {wordShift +=32; y = (int)(word >>>32); }
    if ((y & 0x0000FFFF) == 0) { wordShift +=16; y>>>=16; }
    if ((y & 0x000000FF) == 0) { wordShift +=8; y>>>=8; }
    indexArray = bitlist[y & 0xff];
    word >>>= (wordShift +1);
  }

  private void shift3() {
    int lower = (int)word;
    int lowByte = lower & 0xff;
    if (lowByte != 0) {
      indexArray=bitlist[lowByte];
      return;
    }
    shift();
  }
  ******/

  @Override
  public int nextDoc() {
    if (indexArray == 0) {
      if (word != 0) {
        word >>>= 8;
        wordShift += 8;
      }

      while (word == 0) {
        if (++i >= words) {
          return curDocId = NO_MORE_DOCS;
        }
        word = arr[i];
        wordShift = -1; // loop invariant code motion should move this
      }

      // after the first time, should I go with a linear search, or
      // stick with the binary search in shift?
      shift();
    }

    int bitIndex = (indexArray & 0x0f) + wordShift;
    indexArray >>>= 4;
    // should i<<6 be cached as a separate variable?
    // it would only save one cycle in the best circumstances.
    return curDocId = (i<<6) + bitIndex;
  }
  
  @Override
  public int advance(int target) {
    indexArray = 0;
    i = target >> 6;
    if (i >= words) {
      word = 0; // setup so next() will also return -1
      return curDocId = NO_MORE_DOCS;
    }
    wordShift = target & 0x3f;
    word = arr[i] >>> wordShift;
    if (word != 0) {
      wordShift--; // compensate for 1 based arrIndex
    } else {
      while (word == 0) {
        if (++i >= words) {
          return curDocId = NO_MORE_DOCS;
        }
        word = arr[i];
      }
      wordShift = -1;
    }

    shift();

    int bitIndex = (indexArray & 0x0f) + wordShift;
    indexArray >>>= 4;
    // should i<<6 be cached as a separate variable?
    // it would only save one cycle in the best circumstances.
    return curDocId = (i<<6) + bitIndex;
  }

  @Override
  public int docID() {
    return curDocId;
  }
  
}